2 * SPDX-License-Identifier: BSD-2-Clause-FreeBSD
4 * Copyright (C) 1995, 1997 Wolfgang Solfrank
5 * Copyright (c) 1995 Martin Husemann
7 * Redistribution and use in source and binary forms, with or without
8 * modification, are permitted provided that the following conditions
10 * 1. Redistributions of source code must retain the above copyright
11 * notice, this list of conditions and the following disclaimer.
12 * 2. Redistributions in binary form must reproduce the above copyright
13 * notice, this list of conditions and the following disclaimer in the
14 * documentation and/or other materials provided with the distribution.
16 * THIS SOFTWARE IS PROVIDED BY THE AUTHORS ``AS IS'' AND ANY EXPRESS OR
17 * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
18 * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
19 * IN NO EVENT SHALL THE AUTHORS BE LIABLE FOR ANY DIRECT, INDIRECT,
20 * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
21 * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
22 * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
23 * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
24 * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
25 * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
29 #include <sys/cdefs.h>
31 __RCSID("$NetBSD: boot.c,v 1.11 2006/06/05 16:51:18 christos Exp ");
32 static const char rcsid[] =
36 #include <sys/param.h>
48 readboot(int dosfs, struct bootblock *boot)
50 u_char block[DOSBOOTBLOCKSIZE];
51 u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
54 if ((size_t)read(dosfs, block, sizeof block) != sizeof block) {
55 perr("could not read boot block");
59 if (block[510] != 0x55 || block[511] != 0xaa) {
60 pfatal("Invalid signature in boot block: %02x%02x",
61 block[511], block[510]);
65 memset(boot, 0, sizeof *boot);
68 /* Decode BIOS Parameter Block */
70 /* Bytes per sector: can only be 512, 1024, 2048 and 4096. */
71 boot->bpbBytesPerSec = block[11] + (block[12] << 8);
72 if (boot->bpbBytesPerSec < DOSBOOTBLOCKSIZE_REAL ||
73 boot->bpbBytesPerSec > DOSBOOTBLOCKSIZE ||
74 !powerof2(boot->bpbBytesPerSec)) {
75 pfatal("Invalid sector size: %u", boot->bpbBytesPerSec);
79 /* Sectors per cluster: can only be: 1, 2, 4, 8, 16, 32, 64, 128. */
80 boot->bpbSecPerClust = block[13];
81 if (boot->bpbSecPerClust == 0 || !powerof2(boot->bpbSecPerClust)) {
82 pfatal("Invalid cluster size: %u", boot->bpbSecPerClust);
86 /* Reserved sectors: must be non-zero */
87 boot->bpbResSectors = block[14] + (block[15] << 8);
88 if (boot->bpbResSectors < 1) {
89 pfatal("Invalid reserved sectors: %u",
95 boot->bpbFATs = block[16];
96 if (boot->bpbFATs == 0) {
97 pfatal("Invalid number of FATs: %u", boot->bpbFATs);
101 /* Root directory entries for FAT12 and FAT16 */
102 boot->bpbRootDirEnts = block[17] + (block[18] << 8);
103 if (!boot->bpbRootDirEnts) {
104 /* bpbRootDirEnts = 0 suggests that we are FAT32 */
105 boot->flags |= FAT32;
108 /* Total sectors (16 bits) */
109 boot->bpbSectors = block[19] + (block[20] << 8);
110 if (boot->bpbSectors != 0 && (boot->flags & FAT32)) {
111 pfatal("Invalid 16-bit total sector count on FAT32: %u",
116 /* Media type: ignored */
117 boot->bpbMedia = block[21];
119 /* FAT12/FAT16: 16-bit count of sectors per FAT */
120 boot->bpbFATsmall = block[22] + (block[23] << 8);
121 if (boot->bpbFATsmall != 0 && (boot->flags & FAT32)) {
122 pfatal("Invalid 16-bit FAT sector count on FAT32: %u",
127 /* Legacy CHS geometry numbers: ignored */
128 boot->SecPerTrack = block[24] + (block[25] << 8);
129 boot->bpbHeads = block[26] + (block[27] << 8);
131 /* Hidden sectors: ignored */
132 boot->bpbHiddenSecs = block[28] + (block[29] << 8) +
133 (block[30] << 16) + (block[31] << 24);
135 /* Total sectors (32 bits) */
136 boot->bpbHugeSectors = block[32] + (block[33] << 8) +
137 (block[34] << 16) + (block[35] << 24);
138 if (boot->bpbHugeSectors == 0) {
139 if (boot->flags & FAT32) {
140 pfatal("FAT32 with sector count of zero");
142 } else if (boot->bpbSectors == 0) {
143 pfatal("FAT with sector count of zero");
146 boot->NumSectors = boot->bpbSectors;
148 if (boot->bpbSectors != 0) {
149 pfatal("Invalid FAT sector count");
152 boot->NumSectors = boot->bpbHugeSectors;
158 if (boot->flags & FAT32) {
159 /* If the OEM Name field is EXFAT, it's not FAT32, so bail */
160 if (!memcmp(&block[3], "EXFAT ", 8)) {
161 pfatal("exFAT filesystem is not supported.");
165 /* 32-bit count of sectors per FAT */
166 boot->FATsecs = block[36] + (block[37] << 8)
167 + (block[38] << 16) + (block[39] << 24);
169 if (block[40] & 0x80)
170 boot->ValidFat = block[40] & 0x0f;
172 /* FAT32 version, bail out if not 0.0 */
173 if (block[42] || block[43]) {
174 pfatal("Unknown file system version: %x.%x",
175 block[43], block[42]);
180 * Cluster number of the first cluster of root directory.
182 * Should be 2 but do not require it.
184 boot->bpbRootClust = block[44] + (block[45] << 8)
185 + (block[46] << 16) + (block[47] << 24);
187 /* Sector number of the FSInfo structure, usually 1 */
188 boot->bpbFSInfo = block[48] + (block[49] << 8);
190 /* Sector number of the backup boot block, ignored */
191 boot->bpbBackup = block[50] + (block[51] << 8);
193 /* Check basic parameters */
194 if (boot->bpbFSInfo == 0) {
196 * Either the BIOS Parameter Block has been corrupted,
197 * or this is not a FAT32 filesystem, most likely an
200 pfatal("Invalid FAT32 Extended BIOS Parameter Block");
204 /* Read in and verify the FSInfo block */
205 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec,
206 SEEK_SET) != boot->bpbFSInfo * boot->bpbBytesPerSec
207 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
208 perr("could not read fsinfo block");
211 if (memcmp(fsinfo, "RRaA", 4)
212 || memcmp(fsinfo + 0x1e4, "rrAa", 4)
215 || fsinfo[0x1fe] != 0x55
216 || fsinfo[0x1ff] != 0xaa
219 || fsinfo[0x3fe] != 0x55
220 || fsinfo[0x3ff] != 0xaa) {
221 pwarn("Invalid signature in fsinfo block\n");
223 memcpy(fsinfo, "RRaA", 4);
224 memcpy(fsinfo + 0x1e4, "rrAa", 4);
225 fsinfo[0x1fc] = fsinfo[0x1fd] = 0;
226 fsinfo[0x1fe] = 0x55;
227 fsinfo[0x1ff] = 0xaa;
228 fsinfo[0x3fc] = fsinfo[0x3fd] = 0;
229 fsinfo[0x3fe] = 0x55;
230 fsinfo[0x3ff] = 0xaa;
231 if (lseek(dosfs, boot->bpbFSInfo *
232 boot->bpbBytesPerSec, SEEK_SET)
233 != boot->bpbFSInfo * boot->bpbBytesPerSec
234 || write(dosfs, fsinfo, sizeof fsinfo)
236 perr("Unable to write bpbFSInfo");
243 /* We appear to have a valid FSInfo block, decode */
244 boot->FSFree = fsinfo[0x1e8] + (fsinfo[0x1e9] << 8)
245 + (fsinfo[0x1ea] << 16)
246 + (fsinfo[0x1eb] << 24);
247 boot->FSNext = fsinfo[0x1ec] + (fsinfo[0x1ed] << 8)
248 + (fsinfo[0x1ee] << 16)
249 + (fsinfo[0x1ef] << 24);
252 /* !FAT32: FAT12/FAT16 */
253 boot->FATsecs = boot->bpbFATsmall;
256 if (boot->FATsecs > UINT32_MAX / boot->bpbFATs) {
257 pfatal("Invalid FATs(%u) with FATsecs(%zu)",
258 boot->bpbFATs, (size_t)boot->FATsecs);
262 boot->FirstCluster = (boot->bpbRootDirEnts * 32 +
263 boot->bpbBytesPerSec - 1) / boot->bpbBytesPerSec +
264 boot->bpbResSectors + boot->bpbFATs * boot->FATsecs;
266 if (boot->FirstCluster + boot->bpbSecPerClust > boot->NumSectors) {
267 pfatal("Cluster offset too large (%u clusters)\n",
272 boot->NumClusters = (boot->NumSectors - boot->FirstCluster) / boot->bpbSecPerClust +
275 if (boot->flags & FAT32)
276 boot->ClustMask = CLUST32_MASK;
277 else if (boot->NumClusters < (CLUST_RSRVD&CLUST12_MASK))
278 boot->ClustMask = CLUST12_MASK;
279 else if (boot->NumClusters < (CLUST_RSRVD&CLUST16_MASK))
280 boot->ClustMask = CLUST16_MASK;
282 pfatal("Filesystem too big (%u clusters) for non-FAT32 partition",
287 switch (boot->ClustMask) {
289 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 4;
292 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec) / 2;
295 boot->NumFatEntries = (boot->FATsecs * boot->bpbBytesPerSec * 2) / 3;
299 if (boot->NumFatEntries < boot->NumClusters - CLUST_FIRST) {
300 pfatal("FAT size too small, %u entries won't fit into %u sectors\n",
301 boot->NumClusters, boot->FATsecs);
304 boot->ClusterSize = boot->bpbBytesPerSec * boot->bpbSecPerClust;
313 writefsinfo(int dosfs, struct bootblock *boot)
315 u_char fsinfo[2 * DOSBOOTBLOCKSIZE];
317 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
318 != boot->bpbFSInfo * boot->bpbBytesPerSec
319 || read(dosfs, fsinfo, sizeof fsinfo) != sizeof fsinfo) {
320 perr("could not read fsinfo block");
323 fsinfo[0x1e8] = (u_char)boot->FSFree;
324 fsinfo[0x1e9] = (u_char)(boot->FSFree >> 8);
325 fsinfo[0x1ea] = (u_char)(boot->FSFree >> 16);
326 fsinfo[0x1eb] = (u_char)(boot->FSFree >> 24);
327 fsinfo[0x1ec] = (u_char)boot->FSNext;
328 fsinfo[0x1ed] = (u_char)(boot->FSNext >> 8);
329 fsinfo[0x1ee] = (u_char)(boot->FSNext >> 16);
330 fsinfo[0x1ef] = (u_char)(boot->FSNext >> 24);
331 if (lseek(dosfs, boot->bpbFSInfo * boot->bpbBytesPerSec, SEEK_SET)
332 != boot->bpbFSInfo * boot->bpbBytesPerSec
333 || write(dosfs, fsinfo, sizeof fsinfo)
335 perr("Unable to write bpbFSInfo");
339 * Technically, we should return FSBOOTMOD here.
341 * However, since Win95 OSR2 (the first M$ OS that has
342 * support for FAT32) doesn't maintain the FSINFO block
343 * correctly, it has to be fixed pretty often.
345 * Therefor, we handle the FSINFO block only informally,
346 * fixing it if necessary, but otherwise ignoring the
347 * fact that it was incorrect.